This invention relates to a finally recorded sector detecting system, which is especially suitable for a "write-once" type optical disc device or the like.
FIG. 5 is an explanatory diagram schematically showing recording regions of a conventional write-once type optical disc. That is, in general, the optical disc has an index region and a data region as shown in FIG. 5. A user can record desired data files on sectors (D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, . . . ) in the data region When the files are recorded, index signals corresponding to the files are successively recorded on sectors (I.sub.1, I.sub.2, . . . ) in the index region. Therefore, the latest index signal of the data signal recorded on the disc can be obtained by reading the finally recorded sector (I.sub.2 in the case of FIG. 5) in the index region.
In order to detect the finally recorded sector, heretofore, the amplitude of an RF signal which is obtained by successively reproducing the index signals in the index region is monitored. That is, when a level of the RF signal becomes lower than a predetermined reference value, it is determined that the sector which exists immediately before the sector of the RF signal level change is the finally recorded sector.
That is, in the conventional method, the finally recorded sector is detected from the RF signal level, and therefore the detection of the finally recorded sector is liable to be adversely affected by noises in non-recorded sectors, with a result that the finally recorded sector is not correctly detected.
Furthermore, in the conventional method, even if the index signal written on the finally recorded sector is incorrect, it cannot be detected, and therefore an incorrect index signal may be read out. As a result, it is sometimes the case that a new data signal may be written on the sector on which a data signal has already been recorded, thus erasing the latter data signal.